I just rebuild my 4.3 with a bigger cam, headwork, roller rockers, bigger TBI. It still shifts at 4500rpm WOT but I think with the new setup if could pull longer. What governs this? Is it the Computer determining this? Is it SAFE to shift at a higher speed (700R4 4spd w/OD)

Just wondering what actually governs the redline.. I thought it would shift a bit higher after the work I've done.

 

The shift points are NOT electronically controlled. That didn't start coming into play until the, I believe theyre called, the 4L60E transmissions. The 700-R4 was renamed the 4L60, and the E is for electronic.

Yours is controlled by transmission line pressure, which is adjusted with the TV cable housing. It's bracketed to your intake and the line is connected to your throttlebody. Playing with the line pressure should alter your shift points, although doing this too much can cause major transmission problems, so be careful. And always remember, mark the original cable position so if it gets worse, you can always get it back to where it was.

TV Cable Adjustment

This picture is for a third gen, obviously, but maybe it'll give you a rough idea of what to do.

 

whats a safe way of determing the redline of the engine now thats its been rebuild.

 

there are two red lines, the mechanical limits set by the strength of the parts and the usually lower red line set by the engines ability to move air in and back out of the engine

 

Fooling around with TV cable adjustment to control shift points is a band aid approach that can cause more problems than it solves. WOT shift points are controlled by the governor in the rear of the trans. Swapping governors or just experimenting with different weights & springs will alter shift points. I have used an 87 Vette governor that allowed 5500rpm shifts @ WOT. That was used as a starting point for me & then swapped weights & springs to fine tune it to shift at 5800.

 

I guess my question is: how can I figure out the best shift point withouth blowing up or stressing the engine too much.

 

It's hard to say once you get mods into it. I gauge the powerband just by driving the car. You can feel where the powerband begins, and you can kinda feel when it stops pulling or runs out of steam. When it starts to go soft on you, I'd make your shift point maybe 200 rpms past that....so you get into the powerband good in the next gear since most of us don't have a close ratio 6-speed.

 

drive it you ought to be able to feel when it quits making power, that is where or near where you'd want to shift.

 

Its still pulling pretty good when it shifts, thats why I think it could stand to shift a bit higher.. 4500 is a bit low for an internally modded engine I thought.

 

Agreed. From what I've seen from driving different cars, a very rough "norm" number seems to be around 5500.

 

Nixon 1
I am just wondering what a guy with a mustang is doing i a GM organization? You have to admit, it is odd. So, why? Did you used to have a third gen?

 

Yes he did, IIRC a 6. And what's wrong with guys with Mustangs? Not odd at all to me.

 

Easiest way without hours of experimenting is to locate a shop with a chassis dyno.
Strap it on and let her rip. Otherwise you'll be doing nothing but test runs at the track, shifting at different points to find the highest MPH through the traps.

 

or you could get the governor recalibration kit and change the weights and springs in the governor